Method of epitaxial-like wafer bonding at low temperature and bonded structure

Abstract

A process for bonding oxide-free silicon substrate pairs and other substrates at low temperature. This process involves modifying the surface of the silicon wafers to create defect regions, for example by plasma-treating the surface to be bonded with a or boron-containing plasmas such as a B2H6 plasma. The surface defect regions may also be created by ion implantation, preferably using boron. The surfaces may also be amorphized. The treated surfaces are placed together, thus forming an attached pair at room temperature in ambient air. The bonding energy reaches approximately 400 mJ / m2 at room temperature, 900 mJ / m2 at 150° C., and 1800 mJ / m2 at 250° C. The bulk silicon fracture energy of 2500 mJ / m2 was achieved after annealing at 350-400° C. The release of hydrogen from B—H complexes and the subsequent absorption of the hydrogen by the plasma induced modified layers on the bonding surfaces at low temperature is most likely responsible for the enhanced bonding energy.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a method of epitaxial-like bonding of wafer pairs at low temperature, and more particularly to a method of bonding in which the wafer surfaces are modified to create surface and subsurface defect areas, and possibly amorphized, by ion implantation or plasma, preferably by boron-containing ions or a plasma such as B2H6.[0003]2. Discussion of the Background[0004]For many optoelectronic and electronic device applications, homo-epitaxial single crystalline layers consisting of same material with same crystalline orientation but different doping types or levels are necessary. For some device applications, active layers comprising single crystalline dissimilar materials are required. The active layers should be high crystallographic quality with interfaces that are thermally conductive and almost optical loss free. Conventional hetero-epitaxial growth techniques applied to these lattice mismat...

AI Technical Summary

Benefits of technology

The present invention provides a method for bonding silicon substrates without using external pressure. The method involves preparing the substrates with oxide-free surfaces, creating defect regions in the surfaces, and maintaining the substrates in contact. The bonding process involves plasma treatment of the surfaces, which creates a thin amorphous layer and a monolayer of boron on the surfaces. The substrates can be maintained in contact at low vacuum or in ambient air, and the bonded pair can be annealed at low temperatures. The invention also provides a bonded structure with a first substrate and a second substrate bonded together with an amorphous layer. The method and structure can be used in various semiconductor devices.

Problems solved by technology

Conventional hetero-epitaxial growth techniques applied to these lattice mismatched active layers usually result in a large density of threading dislocations in the bulk of the layers.

To bond wafers composed of thermally mismatched materials, severe and often damaging thermal stresses can be induced with high temperature annealing.

The high temperature annealing process can also produce unwanted changes to bonding materials and often prevents the bonding of processed device wafers.

The bonding materials may decompose at high temperatures, even if the bonding wafers are thermally matched.

The bonding energy of conventional HF dipped hydrophobic silicon wafer pairs is higher than the hydrogen-induced region only after annealing at temperatures higher than 600° C. Therefore, this process does not work for oxide-free hydrophobic silicon wafer bonding.

Therefore, the smart-cut method for a layer transfer using conventional HF-dipped silicon wafer pairs is not possible because the bonding energy is too low at layer transfer temperatures that are lower than 500° C.

Images